The intrinsic thermal properties of luminescent materials (spectral characteristics, relative quantum efficiency, decay lifetime) have important advantages when used as parameters to measure or infer temperature. A large variety of luminescent materials offer good chemical and physical stability, relatively well defined absorption and emission frequency spectra, and intrinsic temperature calibration that is established at the time of chemical synthesis. All of these qualities are conducive to the design and construction of a thermometry system which can include easily interchangeable and potentially disposable thermometer probes--a definite advantage for medical usages. Wickersheim (U.S. Pat. No. 4,075,493) has described a luminescent thermometry system utilizing special phosphors which derive their intrinsic calibration through the ratio of two spectrally distinct emission bands which have separate temperature dependent emission intensities. The use of a system based on a single emission band as well as the time dependent emission properties of luminescent materials for temperature measurement is shown and claimed in a aforementioned copending application now U.S. Pat. No. 4,245,507 ). This patent is incorporated herein by reference in its entirety. The invention disclosed within the present application is unique because it allows the determination of temperature via an intrinsic luminescent property, i.e., characteristic changes in the time dependent emission processes of light emitted in one wavelength band. In practice this can be accomplished using a time varying excitation source and a single detector detecting in one wavelength band. Additionally, this technique can be accomplished using sensitive luminescent materials that are photo-excited with light in the visible rather than ultraviolet wavelengths--an advantage wtih regard to light signal propogation and attenuation in optic fiber bundles.